A high-purity acid-form SL containing composition which is characterized by being substantially free from acetic acid. This high-purity acid-form SL containing composition can be prepared, for example, by a process which comprises: (i) a step of adjusting the pH of a partially purified acid-form SL containing composition so as to fall in an acid region and (ii-a) a step of subjecting the acidified partially purified acid-form SL containing composition obtained in the step (i) to chromatography to recover an acid-form SL fraction, or (ii-b) a step of allowing the acidified partially purified acid-form SL containing composition obtained in the step (i) to stand under low-temperature conditions to recover the formed gel.
